Dye that reacts with the textile fiber to produce both a hydroxyl and an oxygen linkage, the chlorine combining with the hydroxyl to form a strong ether linkage; gives fast, brilliant colors.

Reactive dyes chemically reacted with the fibers with the formation of a covalent bond between the dyes and the fiber. The reactivity of these dyes is due to the chlorine atoms attached to the thiazine ring. When two chlorine atoms are present on the dyes molecules, as in the case of procaine yellow R, one of the chlorine atoms is so reactive, that it reacts with cellulose even at room temperature in the presence of an alkali. Hence such reactive dyes are called cold brand reactive dyes. When only one chlorine atom is present in the dyestuffs molecule, the reactivity of the dye decreases considerably and the dyeing has to be carried out at a higher temperature (65-80 oC). Hence these dyes are called Hot brand reactive dyes.

Fig: Reactive dyes

History of Reactive Dyes

Reactive dyes first appeared commercially in 1956, after their invention in 1954 by Rattee and Stephens at the Imperial Chemical Industries Dyestuffs Division site in Blackley, Manchester, United Kingdom.Reactive dyeing is now the most important method for the coloration of cellulosic fibres. Reactive dyes can also be applied on wool and nylon; in the latter case they are applied under weakly acidic conditions. Reactive dyes have a low utilization degree compared to other types of dyestuff, since the functional group also bonds to water, creating hydrolysis of Reactive Dye.Reactive dyes have good fastness properties owing to the bonding that occurs during dyeing. Cotton is made of cellulose molecules which react with the dye .During reactive dyeing the H atom in the cellolose molecule combines with the cl atom in the dyeing process and results in a bond. Trifunctional dyestuffs also exist.

Uses of Reactive Dye

Reactive dyes are used to dye cellulosic fibres. The dyes contain a reactive group, either a haloheterocycle or an activated double bond, that, when applied to a fibre in an alkaline dye bath, forms a chemical bond with an hydroxyl group on the cellulosic fibre.

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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.